1. Field of the Invention
The present invention relates to a plasma display panel, and particularly, to a plasma display panel which is able to improve color temperature thereof.
2. Description of the Background Art
Generally, a plasma display panel is a display device exciting a fluorescent layer using ultraviolet rays of plasma and displaying an image using visible lights generated from the fluorescent layer.
Important properties the plasma display panel should have are high color temperature more than 9300° K and high contrast ratio. Herein, the contrast means a ratio of brightness on the brightest part and on the darkest part of a screen. The contrast is lowered by near infrared ray or visible light generated from discharge gas inside the plasma display panel or by outer visible light irradiated and reflected from outer side. Therefore, various methods are used for improving the color temperature and the contrast conventionally. Hereinafter, a structure of the conventional plasma display panel will be described with reference to FIG. 1.
FIG. 1 is a cross-sectional view showing a structure of plasma display panel according to the conventional art.
As shown therein, the conventional plasma display panel comprises: a lower insulating layer 9 formed on a lower glass substrate 10; an address electrode 11 formed on a predetermined part of the lower insulating layer 9; a lower dielectric layer 8 formed on the address electrode 11 and on the lower insulating layer 9; a barrier rib 7 defined on a predetermined part on the lower dielectric layer 8 for dividing each discharge cell; a black matrix layer 12 formed on the barrier rib 7; a fluorescent layer 13 formed to have a predetermined thickness on side surfaces of the black matrix layer 12 and of the barrier rib 7 and on the lower dielectric layer 8 for emitting visible lights of red, green, and blue colors by being supplied the ultraviolet ray; an upper glass substrate 2; a sustain electrode 3 formed on a predetermined part of the upper glass substrate 2 so as to cross the address electrode 11 vertically; a bus electrode 5 formed on a predetermined part of the sustain electrode 3; an upper dielectric layer 4 formed on the bus electrode 5, the sustain electrode, and on the upper glass substrate 2; a passivation layer formed on the upper dielectric layer 4 for protecting the upper dielectric layer 4. Hereinafter, operations of the conventional plasma display panel will be described.
As the upper glass substrate 2 and as the lower glass substrate 10 of the conventional plasma display panel, a soda-lime silicate (SLS) glass substrate is used. The lower insulating layer 9 is located on the lower glass substrate 10, that is, the SLS glass substrate, and the address electrode 11 is located on a predetermined part on the lower insulating layer 9.
The lower dielectric layer 8 located on the address electrode 11 and on the lower insulating layer 9 blocks the visible light emitted toward the lower glass substrate 10 direction. Also, a dielectric layer having high reflectance is used as the lower dielectric layer 8 in order to increase a luminous efficiency.
The fluorescent layer 13 consists of red, green, blue color phosphors, and emits visible light having a certain wavelength according to intensity of ultraviolet ray by the plasma which is generated on an area between the barrier ribs 7.
On the other hand, the sustain electrode 3 which crosses with the address electrode 11 is located on lower part of the upper glass substrate 2, that is, the SLS glass substrate, the bus electrode 5 is located on a predetermined part of the sustain electrode 3, and the dielectric layer 4 having superior light transmittance is located on the bus electrode 5. Also, the passivation layer 6 is located on the dielectric layer 4 in order to prevent the dielectric layer from being damaged by the plasma.
After that, when voltage is applied to the sustain electrode 3, a voltage difference is generated between the bus electrode 5 and the address electrode 11 which crosses with the bus electrode 5 in vertical direction. The gas located in an area between the barrier ribs 7 becomes plasma status due to the voltage difference, and therefore, the visible light of a certain wavelength is emitted from the fluorescent layer 13 by the ultraviolet ray generated from the plasma. For example, in the plasma display panel, the discharge gas in a pixel area defined by the barrier rib 7 becomes plasma status by a potential difference between the address electrode 11 and the bus electrode 5. At that time, the fluorescent layer 13 is excited by the ultraviolet ray of the plasma to emit the visible light, and the plasma display panel displays an image using the visible light. That is, the plasma display panel excites the fluorescent layer 13 using the ultraviolet ray generated by Xe gas among the discharge gases such as He gas, Xe gas, and Ne gas which are injected into a discharge space divided by the barrier rib 7, and displays desired color. At that time, it is required that the plasma display panel should have high contrast. That is, the displaying property (that is, the contrast) is improved as the difference between the highest brightness and the lowest brightness becomes larger.
Therefore, in order to improve the contrast of the plasma display panel, a material having superior light transmittance should be used. In order to improve the light transmittance, MgO is used as a material of the passivation layer 6, dielectrics of PbO—B2O3—SiO2 group is used as a material of the upper dielectric layer 4 and of the lower dielectric layer 8.
On the other hand, one of important features the plasma display panel should have is high color temperature. For example, when a signal of white color having no color signal is inputted (that is, R, G, and B signals are all inputted) into a display device such as a monitor and a television, the displayed white color is important for color designing in the display. Generally, the monitor uses color temperature of 9500° K, and the television uses the color temperature of 12000˜13500° K.
Generally, the television displays the white color as a light blue color group to make viewers recognize the white color more clearly, and a projection television uses white color of 6500˜7000° K by the property of a lamp used as a light source and by the efficiency of the system. That is, the color temperature is controlled by controlling white balance, and the color temperature is determined by a luminance and a chromaticity of base color. That is, ratio of R, G, B and color coordinate are determined by the luminance and the chromaticity of the base color, and accordingly, the color temperature is also determined.
The fluorescent layer 13 in the conventional plasma display panel emits visible lights of green, red, and blue colors by vacuum ultraviolet rays having 147 nm wavelength. At that time, an emission intensity of green color is the largest among those visible lights, the emission intensity of the red color is the next, and the emission intensity of the blue color which affects to the color temperature most is the lowest. Therefore, since the emission intensity of the blue color is low in the conventional plasma display panel, the light properties (color temperature) can not help being lowered unless the material of phosphor (fluorescent layer) is improved.
In order to increase the color temperature, the conventional plasma display panel forms the barrier ribs 7 as an asymmetric structure to enlarge emission area of the blue phosphor more than those of the green and red phosphors, and thereby the emission intensity of the blue color visible light is increased relatively more than those of the green and red color visible lights. However, although the above method is able to improve the color temperature and the contrast, item difficulty in fabricating processes is increased and an yield is also lowered.
Also, in another conventional plasma display panel for improving the color temperature, an electric signal which is inputted into a certain pixel is reduced in order to emit the blue color visible light than any other visible lights. However, in this case, the luminance and the contrast are lowered.
On the other hand, other conventional plasma display panel and fabrication method thereof is described in detail in U.S. Pat. No. 5,838,106 registered on Nov. 17, 1998, U.S. Pat. No. 6,242,859 registered on Jun. 5, 2001.
As described above, the conventional plasma display panel forms the barrier ribs asymmetrically to enlarge the emission area of the blue color phosphor in order to improve the color temperature by emitting the blue color visible light more than the red and green color visible lights. Thereby, the item difficulty is increased in the fabricating processes, and accordingly, the yield is decreased.
Also, the conventional plasma display panel reduces the electric signal which is inputted into a certain pixel in order to improve the color temperature by emitting the blue color visible light more than the red and green visible lights, and thereby the luminance and the contrast are reduced.